Permanent canine kidney (MDCK) cells for isolation and plaque assay of influenza B viruses

A wide range of influenza B virus strains with various passage histories uniformly formed well-defined clear plaques with high efficiency in cultures of an established line of canine kidney cells (MDCK). PFU titers of the viruses assayed in MDCK exceeded the titers assayedin ovo. With recently isolated strains such as B/Hong Kong/5/72 and Gifu/2/73, the PFU/EID₅₀ ratios were as high as 100 to 400. MDCK cells have been successfully employed for primary isolation of influenza B viruses from throat washings of patients by direct plaquing.